ARM: dts: meson8b: add ethernet fifo sizes

If unspecified in DT, the fifo sizes are not automatically detected by
the dwmac1000 dma driver and the reported fifo sizes default to 0.
Because of this, flow control will be turned off on the device.

Add the fifo sizes provided by the datasheet in the SoC in DT so
flow control may be enabled if necessary.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>